1. Field of the Invention
This invention relates to gripping apparatus for power tongs and backup tools used in the oil and gas industry.
2. Description of the Prior Art
Power tongs and backup tools are devices used to secure together (make up) and detach (break out) threaded ends of adjacent sections of tubular products such as production tubing, casing or drill pipe by gripping, applying torque to, and rotating one of the sections. A power tong applies torque to one tubular member section to cause it to rotate. A backup tool holds the adjacent tubular member section much as pipe wrenches are used often in conjunction with a power tong to grip and prevent rotation of the adjacent sections of tubular product. A backup tool is also capable of applying torque to the tubular product section.
Conventional power tongs and backup tools used in the oil industry often damage the tubular sections. In recent years, major oil companies have required that strings of tubular products must be coupled ("made up") and decoupled ("broken out") with a minimum of (i) damage to the tubular products from teeth marks; (ii) deformation of the tubular products; and (iii) cracking of cement or plastic coating on the inside of the tubular products. The goal of these requirements is to minimize concentrations of corrosion and stress on the tubular products resulting from the tears and gouges caused by the gripping teeth of power tongs and backup tools. Also, to maintain integrity of the threaded connection it is desirable to reduce deformation of the pipe by the power tong and backup tool near the location of threads during makeup to assume more compatible meshing of the threads of adjacent products and reduce frictional wear.
U.S. Pat. No. 5,172,613 issued Dec. 22, 1992, entitled "Power Tongs with Improved Gripping Means" ("Wesch I") and U.S. Pat. No. 5,542,318 issued Aug. 6, 1996, entitled "Bidirectional Gripping Apparatus" ("Wesch II") are incorporated herein for all purposes. The Wesch I patent discloses a cam ring turned against a concentric drag ring which moves the gripping assemblies into and out of contact with the tubular surface of the pipe. The Wesch II patent discloses bidirectional gripping assemblies having a double-seated linkage which supports a pivoted jaw within a housing so that the jaw may be used to grip a pipe and exert radial force thereon to hold the pipe against the torque applied in opposite directions. U.S. Pat. No. Re. 31,993 (also incorporated herein by reference for all purposes) issued Oct. 1, 1985, as a reissue of U.S. Pat. No. 4,281,535 describes apparatus to accomplish the task of making and breaking of threaded joints tubular products using wrap-around pivoted jaw assemblies.
Generally, gouging and tearing of pipe is caused by (i) ineffective gripping assemblies; (ii) gripping jaws having insufficient gripping force; of (iii) the gripping surface or the teeth. These conditions can over-stress the pipe when radial force is applied in addition to the torsion force required to either hold or apply torque to the tubular member. The gripping surface (wheather teeth or any other friction surface which increases the coefficient friction between the gripping assembly and the pipe) must be designed to substantially conform to the outer surface of the pipe even though the pipe may not be round or the tong may not be located transversely to the pipe at the time of gripping. Any improper alignment causes reduced contact areas between the pipe and gripping system. Thus it is important that proper alignment be maintained.
Conventional clamp backup tools apply gripping force to jaws by with hydraulic rams or arms actuated directly by hydraulic rams. It has been demonstrated that counterforces on the jaws caused by applied torque may compress such oil in the hydraulic rams sufficiently to cause skidding of the pipe on the gripping surfaces. Even at 3,000 P.S.I., oil is soft compared to the mechanically applied gripping force discussed herein.
Normally, conventional tongs and backup tools do not apply the gripping force evenly around the pipe. Instead, it is applied to areas around the pipe which are insufficient to minimize the causes of deformation and teeth marks on the surface of the pipe. The balanced pivoted jaws of U.S. Pat. No. Re. 31,993; U.S. Pat. No. 5,172,613 and U.S. Pat. No. 542,318 solve these problems.
U.S. Pat. No. 5,669,653 discloses a backup tool in which a cam wedge is pushed by a fluid cylinder using pivoted jaws. FIG. 3 of U.S. Pat. No. 4,463,635 also discloses a tool having a wedge block which uses a roller to operate two arms to grip a cylinder. Since the wedge is pushed in the tool disclosed in U.S. Pat. No. 5,669,653 in order to cause gripping of a tubular member, the backup tool is unusually long and cumbersome to mount on the power tong. U.S. Pat. No. 5,669,653 also shows the actuating fluid cylinder with two bolts or pins at its base. Seldom is oil field pipe truly round. Accordingly, if an egg-shaped pipe cross section is gripped, side load is transferred to the wedge and therefore to the fluid cylinder.